Introduction: The aim of this study was to identify and characterize subclinical synovitis in patients with rheumatoid arthritis (RA) in clinical remission using power Doppler ultrasound (PDUS) and serum levels of biomarkers of inflammation and/or angiogenesis. Methods: We selected patients with RA in clinical remission defined as a Disease activity score of 28 joints (DAS28)-erythrocyte sedimentation rate (ESR) <2.6 for more than six months tested by two independent rheumatologists. Clinical, epidemiological, demographic and serological data were analyzed. PDUS of knees and hands was performed by a sonographer. Synovial hypertrophy (SH) and PDUS signal were scored (grades 0 to 3). SH ≥2 and a PDUS signal was classified as active synovitis. Serum levels of biomarkers of inflammation/angiogenesis were determined by Quantibody® Human Array. Results: This study included 55 patients, of whom 25 (45.4%) met criteria for ultrasound-defined active synovitis. Patients with active synovitis had higher DAS28-C reactive protein (P = 0.023), DAS28-ESR (P = 0.06), simplified disease activity score, SDAI (P = 0.064), and only 12% were taking oral glucocorticoids (≤5 mg/day) compared with 40% of patients without active synovitis (P = 0.044). Patients with synovitis also had significantly higher serum levels of the angiogenic biomarkers angiopoietin-2 (P = 0.038), vascular endothelial growth factor-D (P = 0.018), placental growth factor (P = 0.043), stromal cell-derived factor-1 (P = 0.035), matrix metallopeptidase-2 (P = 0.027) and basic fibroblast growth factor (bFGF) (P = 0.007), but not of pro-inflammatory cytokines.In the multivariate logistic regression model used to explore prognostic biomarkers for active synovitis, serum levels of bFGF, DAS28-ESR and not receiving glucocorticoids were the best predictors of active synovitis. The predictive indexes provided by the model were specificity 73.3%, sensitivity 72%, and area under the curve in receiver operating characteristic 81.5% (95% CI: 70.1% to 92.8%). Conclusions: Nearly half of the patients with RA in clinical remission had ultrasound-defined active synovitis, higher disease activity and less frequent oral glucocorticoid consumption than patients without active synovitis. This clinical situation was associated with a specific biological profile characterized by an excess of angiogenic mediators rather than persistent proinflammatory cytokine responses.